1. Field
Embodiments described herein relate generally to an MRI (magnetic resonance imaging) apparatus and an MRI method.
Additionally, embodiments described herein relate to technology to apply a prepulse such as a presaturation pulse which saturates nuclear spin in an application region and an inversion recovery pulse (hereinafter referred to as an IR pulse).
2. Description of the Related Art
MRI is an imaging method which magnetically excites nuclear spin of an object set in a static magnetic field with an RF (radio frequency) signal having the Larmor frequency and reconstructs an image based on nuclear magnetic resonance signals (hereinafter referred to as MR signals) generated due to the excitation.
An MRI image can include a motion artifact caused by a voluntary or non-voluntary movement of a body tissue. A cyclic movement, such as pulsation of a vessel, can produce a ghost in the image in a certain direction (a phase encoding direction) depending on the imaging condition. A non-cyclic movement, such as swallowing and respiration, can produce parallel stripes in a certain direction (a phase encoding direction) or a blur in the image. These artifacts can be falsely recognized as a lesion and lead to an erroneous diagnosis.
Thus, in normal MRI, in order to improve the image quality, MR signals from a particular region where a motion causing an artifact occurs are suppressed by applying a presaturation pulse to the particular region before application of an excitation pulse for collecting MR signal data.
A known conventional technique using the presaturation pulse is disclosed in Japanese Patent Laid-Open No. 2008-289862. The MRI apparatus described in Japanese Patent Laid-Open No. 2008-289862 displays an application purpose and application efficacy for each prepulse at the time of setting of imaging conditions and determines the order of application in a case where a plurality of prepulses are applied.
The determination of the order of application is made by considering that the presaturation pulse applied last has a greater signal suppressing effect than the other presaturation pulses. This facilitates setting of the plurality of prepulses that have different purposes, such as water excitation and fat suppression.
The invention disclosed in Japanese Patent Laid-Open No. 2008-289862 has good advantages as described above. However, in actual imaging, many imaging conditions other than the order of prepulse application also have to be set. Specifically, an operator has to set not only imaging conditions for the essential region of interest but also imaging conditions for a prepulse intended to reduce an artifact or otherwise improve the image quality. For example, in imaging of a spine, a motion artifact occurs due to a respiratory movement of the abdomen or pulsations of the great cardiac vessel in front of the spine. Thus, an application region for a presaturation pulse to reduce the motion artifact has to be set.
Since the MRI apparatus can separately take images of an artery and a vein by using a labeling technique, such as a time spatial labeling inversion pulse (t-SLIP) method, the MRI is considered effective for diagnosis of a renal artery, for example. However, the imaging conditions are complicated because application regions for a plurality of prepulses including a region-selective IR pulse applied as a labeling pulse and a presaturation pulse have to be considered in combination with positioning for imaging.
Thus, there is a demand for a technique that facilitates setting of an imaging condition concerning a prepulse compared with conventional technique.